In a typical wireless communication system such as a code division multiple access (CDMA) cellular radio frequency (RF) radiotelephone system, a communication unit such as a base station having a controller and a plurality of transmitters and receivers communicates with a switching center and with a mobile communication unit operating within an area served by the base station.
Designing a wireless communication system requires selecting geographic locations of base stations and their desired service areas, and ensuring that certain radio frequency channels, such as pilot, page and synch channels, are present within each service area, while interference with other service areas is minimized.
Typically, pilot-channel powers at each base station are manually adjusted, while page- and synch-channel powers are automatically scaled to the adjusted pilot-channel power levels. Traffic-channel power limits may also be automatically scaled to the pilot-channel power levels. For simplicity, pilot-, page- and synch-channel powers are referred to collectively herein as pilot-channel powers, although it is contemplated that the term pilot-channel power may apply to only one or any combination of such channels or to any similar type of channel. Although it is possible to select a specific pilot-channel power, prediction of the actual signal propagation pattern of the pilot-channel may be difficult where the signal may be reflected in unanticipated directions, resulting in insufficient signal strength in a base station's designated service area and/or unacceptable levels of interference in neighboring service areas. For example, setting one or more pilot-channel powers too high may cause too many pilot-channel signals to be present a various locations throughout the system, and may hinder a mobile communication unit's ability to select the best pilot-channel from a pathloss perspective, which may detrimentally affect soft handoff performance of the system. It may also cause the signal-to-noise ratio from all of the pilot-channel powers at a particular location to be unacceptable.
Moreover, it may be time consuming and expensive to manually select and field test different combinations of pilot-channel powers to obtain complete coverage and acceptable interference levels for each service area in the communication system.
There is therefore a need for a method for selecting channel powers in a wireless communication system which automatically evaluates the effects of setting an individual pilot-channel power on the entire wireless communication system, which results in a near optimum number of pilot-channels being available at critical points in the system, and which minimizes levels of interference within the system.